Shielded spark plug



May' 22, 1934. G. M. PAULSGN y 1,959,442

SHIELDED SPARK PLUG Filed Septa 8, 21952 2 SheetsuSheet E.

May 22 l934- G. M. PAULSON 1,959,442

SHIELDED SPARK PLUG Filed Sept. 8, 195.2

2 Sheets-Sheet 2 .3l I y 39 36 44 E j )Mr/jvolfE/vTo/e i- Patented May I I u j l UNiTED-STATES PATENT, fopplcg.

l.SHIELDED SPARK PLUG lGeorge M. Paulson, New York, N. Y.,l assigner 'to The B. G. tion, New York, N. Y., a corporation of New York Application September 8, 1932, Serial No. 632,090 1 1 Claims. (Cl. BB3- 189) The invention relates to spark-plugs which are In former lradio-shielded constructions the shielded against the elements and oil, and lt also shields have been applied to the outside of the and more especially relates to spark-plugs which bodies of the plugs. or have been connected to the are shielded electrically to prevent the disturbplugs by balls. or lock-nuts, or screw-threads or a ances set up by the ignition current from adbayonet-type connections. which limit the con- 60 versely ailecting radio equipment carried by the ductor to one position or which cumber the sparkairplane or vehicle. plug itself with attachments which are trouble- The invention is more particularly intended some when it comes to replacing s. sparkplug. v for aviation spark-plugs. 'In many airplane en- Brleily stated, a salient feature of this invenlo gines, other engine parts and accessories come so tion is that the connection between the shield and ed close to the spark-plugs that former shielded conthe spark-plug is brought downl inside the "hex e structions are either unavailable or the applica of the body of the plus. thereby making possiblel tion and removal of the shield would be-very'dimthe aliment possible construction. Anotherim-l cult. l portant feature 'is that the connection is made by `1li An important object, therefore. of thisv invenl. direct thrust of the lower end of the shield into 70; tion is to provide a short or low, and compact, Becket in the iop 0! the Plug body. whereupon a shielded spark-plug which occupies but little room resilient loekinl etiOn iekeS Place that 1101i! the ,outside the engine. A further object is to make Shield and the conductor in place without any it possible to apply and to remove the shield with- DOSSibility 0i loosening or coming apart, but Der- 20 out removing the spark-plug and-with theV mlm.. mits the connection to be separated when desired. 7

mum of overhead clearance.

A further object is to provide for the tight and or absolutely tight against water or o'il.

spark-p1ug, and for its removal, inthe most conbe apparent t0 iihOSe Skilled in the art.

2Q venlent manner, and also to permit the shield to The parte end Comblniiions '0f Darts 00118151- an, be turned about the axis of the plug while the tilting' the inventionfwill be described and then shield is in full engagement. An object is to pro- Pointed Olli in the elimsvide a simple and effective type of connection-be- In the `ailefiinlnylngl drWiHGS. Yforming Dart tween the shield and the plug, which makes it hereof: y

t ao possible te dispose e laterally entering conductor Fis-1 is a Side elevation 0i a spark-plus, shield. es

1n am, direction about the and shielded "conductor assembled. the illustra- A further object is to provide s construction tion beine oi'api'eierred embodiment or the invenand manner of connecting the shield removably to M0113 the spark-plug such that when tne shield is taken F18- 2 i8 a vertical section:

I 354 oil' the spark-plug can kbe 4treated like a vregular Fig' 3 is horizon@ SeCiilOn taken 0n il'ierllliiil()v v spark-plug. Afurther object is to devise the part- 3 3 0l' FS- 33 of the connection which is carrledby the spark- Fig- 4 is horizont Section teken through the plug itself in such n wey that it deesnoi interfere mid-Portion 0f the Shield: and

A in any way with the application of'a wrench to Fig- 5 1S 3 fragmentary elevtln Showing the Q the body of the plug, when a sparbplug 1s taken terminal construction which islocated inside the as out or the engine or put in. f shield. the insulating bushmg being in section. Another object is to provide an improved man- The Consmllctlon 0f the Spark-P1118 Proper,

ner of securing a shielded and insulated conducwhich 1s designated by the numeral 2 may be tor to aspark-plug shield and for electrically cnnvaried in numerous particulars without departing 45 neeting `the eendueiorehieiding te the v:newline from the invention. Except for the matters 10oV plug shield.

yAnother object 1s to provide the sparbplug trated is one that is known. 'Ihe body` 3 of the shield with a terminal which automaticallyfmakes plus is the part that is screwed into and out of reliable contact with the top of the spark-plug the engine Opening. This part of a spark-plug 50 when the shield is inserted in place. A further iS 8150 frequently termed the shell. It has the 105 u object is to providea spark-plug shield which customary external screw-thread 4 on its lower does not have to be taken apart ywhen applying portion to engage the engine opening, and at the it or removingit from the spark-plug. top it has a polygonal portion 5 to take a wrench.

- Another object is to provides. spark-plug shield In the spark-plug of the present invention, this 56 of simple, durable and economical construction. portion is extended upward and made larger or 110 body has an internal screw-thread to receive a nut 6, which is screwed into the body from the top. This'nut is a preferred element or means for holding the core in the body and also for producing a gas-tight joint between the spindle and the surrounding rolled mica insulation '1. The term. core may be used for convenience as including the spindle as well as 4the insulating portions of the spark-plug proper. The particular construction shown is one in which a stack of mica washers 8 is held under compression between the 'head 9 at the lower end of the spindle and a compressible metal sealing ring which is forced upward in a taperedopening of the nut 6, another stack of mica washers 10 being held under compression between the top of the nut and an upset retaining means at the top of the spindle. This part of the core extends above thebody of the plug in the usual manner. In place of the customary top button against which the upper end of theA spindle'is usually upset, I provide the plug for the purpose of this invention with an electrical terminal comprising to an outwardly and downwardly sloping contact face 12, which extends entirely around the annu'- lus. This face is preferably concavely curved in any vertical axial plane, as shown.

As previously stated, the hex made wider than usual. It also extends somewhat above the nut 6, whereas ordinarily the nut projects above the shell. A very important new feature is that the hex or top of tht` body is made with a broad internal recess 14, the wall of which is spaced away from thecore, and,

in this construction, away from the hex top 15 of the nut, the interior of the recess being, therefore, much wider than the internal, threaded portion of the body which ample width of the recess 14 permits the nut to be engaged by a socket wrench when the spark-plug proper is assembled, or in case it should be necessary to take the boundary wall of the recess should be suiiiciently spaced from the core or other internal parts extending upward into andthrough the recess so that the shieldvlG can be applied and removed without interfering with any such parts.

The shield 16 is preferably a squat ball-like shell, made of two sheet metal parts permanently united by a joint 1.8 at approximately the midhorizontal plane. A metal connection thirnble 19 is'held rmly at 20 This thimble extends laterally from the shield, but by laterally it is not necessarily meant that' the thimble is disposed at right-angles to the axis of the spark-plug, as it is shown, since it may also be disposed at an upward inclination.

The bottom of the shield is formed with a short neck 22 of such diameter that it can be forced within the bounding wall of therecess or socket 14 of the body of the spark-plug 2. This neck is subdivided by numerous vertical slits 23, to form many resilient fingers 24. 'The lower ends of these fingers are crimped outward in the shape of a rounded bead 25, tosnap or spring into a circular` groove 26 in the lower portion of the bounding wall of the socket 14. The form of the locking elements 25 makes it possible to enter them -in the top of the socket by a direct push on top of the shield. As the fingers enter they are squeezed inward, and when the shield is all the way home, they spring outwardinto locking engagement with the groove. The lock is a tenacious one,but notwithstanding this,the shield can vtend to lose their springiness. To overcome that a beveled annulus 11. shaped 5 of the body is boundary receives the nut'. The.

plug apart. In any event the" in an opening in the shield. Y

wider' than is ordinary. The mid-portion of the be removed without undue effort. The resilience of the metal of the fingers could be relied upon` solely for the locking action, but after numerous applications and removal of the shield they would 1 8U dimculty, I have provided a spring wire 28 curved to form a split ring, which is sprungA into the discontinuous internal. groove formed by the beads of the fingers 24. This spring wire, thus held, requires no other means to keep it from coming out when-the shield is oi the plug, and it greatly prolongs the useful life of the nngers. It will be understood that the importance of a secure lock between the shield and the sparkplug is not merely to keep the shield from getting loose or becoming accidentally detached, but to preserve the electrical connection between the wire 29 of the conductor 30 and the central electrode of the spark-plug, and to also preserve the electrical shielding connection between the metallic shielding 32 oi the conductor, through the metal shield 16 to the grounded body of the spark-plug.

From the l foregoing it will be evident that the invention provides a very short shielded sparkplug construction, and one in which the shield can be taken oi and put on with but little headroom. Because of the exibility of the neck or ngers of the shield, the neck can be cocked or tilted when the snap-lock is not actually in engagement. Thus,the shield can be taken ofi by a rocking movement when the projections 25 have beenV pulled out of the groove 26, and the neck 'caribe entered in a similar manner, it it should befound more convenient to avoid obstruction ,in this manner.

The construction also permits the shield to be applied in any position of rotation about the axis, or to be turned to any position desired after it is securely locked, in order properly to orient the lateral conductor. Strength, simplicity, reliability, fiexibility, cheapness and convenience of the means for detachably assembling the shield and the spark-plug are objects that have been sought. When the shield is in place it is virtually one with the spark-plug, and when the shield is removed the spark-plug proper is left as its own unit and can be dealt with like an ordinary sparkplug. The spark-plug itself has no extraneous devices, and can be taken out of the engine and put in, and can be assembled and disassembled, as easily as an ordinary spark-plug.

The large hex section 5, which is extended upward from the body of the spark-plug around the core to provide a socket for the reception of the neck of the shield, has a further advantage, which is that it gives additional radiating surface and helps materially to cool the plug.

The conductor 30 is of a known kind having insulation 31 about the wire, a metallic braided shielding 32 about the insulation, and a fabric braiding. 33.0ver all. The cable is prepared by cutting the outside fabric back a considerable v distance from the end of the wire, cutting the metallic shielding 32 back a shorter distance from the end, and cutting away the insulation so that a short portion 34 of the wire is left projecting.

The portion of the insulated conductor from which the braidngs have been removed is inserted through the connection thimble 19 'and through an insulating bushing 36, which is held in the thimble and projects into the interior of the shield.

The automaticv contact-making terminal of the shield, constituting an important feature of 15() between the disc 38 and a flange 44 on the invention, is preferably contrived in the lowing manner: An apertured disc y38 is sprung into a groove in the bore of the bushing 36, near its inner end. A small metal collar 39 Vis held in the aperture of this disc, projecting forward. The projection 34 `of the stranded wire isl passed through this collar and its strands are bent back over the forward end of the collar to establish electrical connection between the conductor and the collar. This is sufficient to insure good connection at this point, but naturally additional means may be used if desired.

The terminal proper is formed of a piece of resilient wire closely coiled to form a head 40, preferably of a somewhat conical shape, to make good contact with the face i2 of the annulus 11 as the result of merely pushing the shield 16 into engagement witht he body of the spark-plug. A limb 4l of this terminal extends rearward from the head and is given a turn about the'collar 39, the collar. By upsetting the rear end of the collar against the back of the disc, the collar is secured in place and also the limb of the terminal is anchored.

'I'he manner of securing the conductor and of making electrical connection between the shield 16 and the shielding 32 of the conductor remains to be described.

The outer end of the connection thimble 19 is screw-threaded on the ,outside to receive a coupling nut 46. On the inside, this end of the thimble is formed with a back end of the metallic braiding 32 is turned back over a tapered wedge ring 48, which is forced by the nut 46 into the tapered recess, thereby strongly gripping the metallic braiding to the metal thimble and likewise firmly holding the conductor so that it can not pull out.

fol-

While the preferred embodiment of the inven-I tion has been described in detail, it will be understood that many changes in form and detail may be made without altering the substance of the invention or particular features thereof.

It may be stated that the sparking points or grounded electrodes 50 and the central electrode 51 are of novel construction, but since these are claimed in a separate application it is unnecessary to describe them here.

I claim:

1. The combination with a spark-plug the body of which is so formed as to provide a rigid socket in its top, of a sheet metal shield having an entering neck constructed for rotary, resilient, separable, interlocking engagement with said socket.

2. The combination with a spark-plug having a body, the top of which is formed with a socket having a circular groove, of a shield having a socket-entering portion subdivided into resilient fingers which are provided with formations to interlock removably with said groove.

3. The combination with a spar -plug having a body, the top of which is formed with a socket having a circular groove,of a shield having a socket having a circular groove, of a shield having a socket-entering portion subdivided into resilient ngers which are provided with formations to interlock removably with said groove, and a resilient element swung into all said formations to give life to the fingers.

4. A spark-plug having a body, the lower portion of which is externally threaded to engage the engine opening, the middle portion of which is internally threaded to receive a nut, and the upper portion of which is externally polygonal to take a wrench, this polygonal portion having a tapered recess 47. The cutwide recess to form a socket for a detachable shield, the bounding wall of said recess being much larger in diameter than the threaded interior of the body below the recess.

5. A spark-plug having a body, a spindle, insulation about the spindle, and a beveled annulus about the upper end of the spindle, which is upset to grip said annulus against the top of the insulation, the top of said body being formed with a recess, in combination with a shield having means to receive a laterally entering conductor, and a resilient terminal within said shield to make automatic contact with said annulus when the lower end of the shield is inserted in said recess.

6. A spark-plug shield comprising a metallic shell having a neck at the bottom adapted to engage a socket in the body of the spark-plug,

a lateral connection thimble of conducting material held in an opening of said shell, an insulating bushing in said thimble and projecting' into the hollow interior of the shell, said b adapted to receive an insulated conductor, and a terminal comprising a coiled head and a resilient limb, the latter secured in 7. A spark-plug shield comprising a metallic shell having a neck at the bottom adapted to engage a socket in the body of the spark-plug, a. lateral connection thimble of conducting material held in an opening of said shell, an insulatinterior of the shell, receive an linsulated conductor, a small metal collar held in the inner end of said bushing and adapted to receive the bare portion of the conductor, and a resilient wire terminal secured to said collar and having a coiled head.

8. A spark-plug shield comprising a metallic shell having a neck at the bottom adapted to engage a socket in the body of the spark-plug, a lateral connection thimble of conducting material heldin an opening of said shell, an insulating bushing in said thimble the hollow interior of the bushing, a small metal collar projecting from .said disc, and a resilient, coil-headed terminal,

said collar being upset to grip the collar and the limb of said terminal to said disc.

9. 'Ilie combination with a spark-plug, of a metal shield applied to the metal body of the spark-plug, said shield having a connection portion which is externally threaded and formed internally with a tapering socket, an insulated conductor inserted in said connection portion and having a metallic shielding, a nut to engage the external threads of said connection portion, and a tapered annular wedge forced into said tapered recess to grip a turned-back portion of the said metallic conductor shielding and to secure the conductor in said connection portion.

l0. A radio-shielded spark-plug, comprising a spark-plug having a body and a core, said body having an enlarged wrench-receiving portion which is recessed to form a rigid socket surrounding and spaced from the core, and said core extending above said socket and provided at the top with a terminal, in combination with a shield comprising a metal shell enclosing and extending over the upwardly projecting portion of the..

the body of the spark-plug, said neck being resilient and the neck and socket being so the bushing.

` ward pressure of the neck Iormedvas to constitute a locking it' detachably in swivel engagement with the socket,l and a resilient terminal firmly supported in the shell in electrical connection with the conductor and in- -sulated from the shell and adapted to make electrical contact automatically with the terminal 'of theV spark-plug when the neck o! the shell is thrust into the socket. I

1l. A radio-shielded spark-plug, comprising a spark-plug. having a .body and a core, said body having` an enlarged wrench-receiving portion which is recessed to form a socket surrounding and spaced from the core, and said core extending-,above said socket and provided at the top with a terminal, in combination with a shield lcomprising a metal shell enclosing and extending over the upwardly projecting portion of the core Imi swivel connection. outfand having means to receive a laterally entering conductor, said shell having a bottom neck to t within said socket in electrical contact with the body or the spark-plug, said socket and neck `being provided with a circular groove and resilient portions to engage the same so as to constitute a detachable and swiveling connection, said shield having a lateral opening. a metal thimble secured to the shell at said opening and adapted to be electrically connected .with the metaleshielding of an insulated conductor, a rigid insulating bushing in said ythimble for the reception of the conductor, and a resilient terminal carried by said bushing and adapted to make contact automatically with the terminal of the spark-plug when L the neck of the shell is thrust into the socket.

GEORGE M. PAULSON. 

